The present invention relates generally to an improved control system for a laser enhanced transluminal catheter device, and more particularly to a such a control system utilizing an optical feedback system capable of monitoring the output intensity or energy of the laser beam at the distal tip of the catheter. The feedback signal is normalized relative to that level detected at a point disposed relatively close to the laser generator component per se.
The control system of the present invention is particularly adapted to a laser enhanced transluminal angioplasty catheter wherein obstructions in blood vessels may be treated with exposure to laser energy to obtain either a partial reduction and/or elimination of the obstruction by means of such exposure. An optical fiber is utilized for transmitting the laser beam energy from the generator onto the obstruction located in the zone to be treated. The optical fiber can also be utilized for the purpose of providing illumination and optical viewing. Laser enhanced transluminal angioplasty catheter devices are considered valuable tools for the treatment of commonly encountered forms of arteriosclerosis and the like.
Atheroclerosis is among the more commonly encountered forms of arteriosclerosis as it relates to the human heart and circulatory system, which typically has been treated by drugs, angioplasty catheterization, and also through open heart bypass surgical procedures. Of these various forms of treatment, angioplasty catheterization has been found to be a treatment of choice in certain situations. Such treatment normally involves initially bringing a balloon-tipped catheter proximate the material forming the obstruction matter in the vessel, with the distal tip catheter normally being forced through the obstruction and the balloon portion is thereafter inflated so as to cause dilation of the obstruction. This procedure is effective in reopening the blood vessel and restoring substantially normal circulation in many cases. This procedure is, however, especially dependent upon the skill of the cardiologist, and particularly as that skill pertains to manipulation and ultimate direction and control of the catheter. Normally, some assistance is provided through fluoroscopy techniques, typically through the incorporation of radiopaque members along the catheter. It is further recognized that angioplasty catheterization is frequently a procedure limited to those patients having obstructions which have not totally occluded the blood vessels to the point where the nominal diameter of the distal tip of the catheter would otherwise prevent passage of the catheter through the obstruction prior to dilation of the vessel.
Because of its application to surgical procedures, laser enhanced transluminal angioplasty catheters have been developed. In such devices, the catheter is provided with a source of laser energy, and this laser energy is directed to the site along optical fibers. One such laser enhanced transluminal angioplasty catheter device is disclosed in copending application, Ser. No. 560,234, filed Dec. 12, 1983 and entitled "LASER TRANSLUMINAL ANGIOPLASTY CATHETER" and assigned to the same assignee as the present invention.
By way of background, dilating catheters are known, having been disclosed in U.S. Pat. Nos. 4,040,413; 4,271,839; and 4,299,226. Catheter devices including optical fibers are disclosed in U.S. Pat. Nos. 3,123,066; 3,136,310; 3,858,577; 4,146,019; and 4,273,019. Also, laser enhanced catheters are disclosed in U.S. Pat. Nos. 3,467,098; 3,538,919; 3,843,865; and 4,266,548.
As set forth in co-pending application Ser. No. 560,234 described above, a laser transmitting transluminal angioplasty catheters is disclosed. An additional example of multi-technology catheters is described in U.S. Pat. No. 4,207,874 and/or the American Journal of Cardiology, 50:80, 81 (Dec. 1982). In U.S. Pat. No. 4,207,874, and of which the American Journal of Cardiology article is an elaboration, a fiber optic directable catheter is disclosed, with the device including a bundle of laser transmitting fibers and a centrally disposed lumen for permitting the suction removal of vaporized waste material after exposure to laser beam energy. Upon completion of the tunneling procedure, blood samples which are collected in a transparent external collection reservoir visually indicate the extent of completion of the procedure to the operator.
In laser enhanced transluminal angioplasty catheter devices, it is desirable for the operator to determine and to be reasonably confident that the laser energy being directed to the site is within certain predetermined desirable limits, that is, the energy is known to exceed a certain base or minimum threshold level, while not exceeding a certain upper limit. An indication that the laser beam energy is within predetermined limits will enable the procedure to be more reliable, expedient, reproducible, and efficacious. Inasmuch as optical fibers are being employed, along with other electro-mechanical and optical systems, proper evaluation of the operating parameters is desired. For example, the rupture, fracture, or occurrence of damage to the optical fiber may reduce the energy level available at the distal tip of the catheter to such an extent that the procedure would be generally ineffective. On the other hand, excessive quantities of laser beam energy available at the distal tip of the catheter may adversely affect the quality of the procedure.
The present invention utilizes a control system which is interposed along the optical fiber segments which are provided to transmit laser energy from the generator to the distal tip. The control system includes an electromechanical shutter and a beam splitter disposed along the beam path. An attenuator and a focusing lens are located orthogonal to the energy beam, and a predetermined proportion of the energy is reflected and/or sampled by the beam splitter and directed into the attenuator and focusing lens and onto a first detector. The detector is in turn coupled to a power level monitor. On the catheter side of the beam splitter, and also orthogonal to the beam, is an interference filter and a second focusing lens. At the distal tip of the optical fiber there is disposed a fluorescent element. The term "fluorescent" is intended to be used in a comprehensive sense, such as the response generated in such an element when irradiated with electromagnetic radiation of a given wavelength, with the response being the emission of radiation at a second and longer wavelength. One particularly desirable optically reactive device is a sapphire doped to fluoresce when transmitting laser energy. Since the fluorescent energy which is generated by the incident laser energy is at a wavelength significantly different from that of the laser energy, the fluorescent energy is transmitted or reflected back through the optical fiber and onto the catheter facing surface of the beam splitter. The fluorescent energy is then reflected by the catheter facing surface of the beam splitter (dichroic filter) into a focusing lens and thence onto a second detector. The output of the second detector is typically amplified and fed into a threshold detector. The output of the threshold detector is, in turn, coupled to the shutter system as well as to the power supply of the laser generator.
In the event the distal portion and/or distal tip of the optical fiber becomes damaged, the quantity or output of fluorescent energy generated by the optically reactive means will become diminished and the threshold detector will respond to the drop with a reduction in signal amplitude. This change, as detected, will create a signal which may be fed through a feedback loop which will, in turn, either shut off the laser generator and/or close the shutter system. The system of the present invention permits simultaneous monitoring of the output of the laser generator and the output of the optical fiber. In certain applications, an attenuator may be placed in the laser beam path in front of the shutter system. The ratio of the optical fiber output relative to the laser generator output is monitored continuously, and in the event the ratio falls outside of a predetermined range because of a failure of a system component, the entire system may be automatically shut down.